Nb on Al₂O₃ and doped-Si as cryogenic light detectors

For rare event searches, such as the direct dark matter search experiment CRESST (Cryogenic Rare Event Search with Superconducting Thermometers), highly sensitive cryogenic detectors are indispensable. A very low energy threshold (≪100eV) and excellent energy resolution are required to increase the experimental sensitivity, particularly for low mass dark matter particles (m_DM<5GeV/c²), and to differentiate between these rare events and natural radioactive backgrounds. For background suppression, CRESST benefits from using simultaneously two detection channels from scintillating calorimeters, in this case of heat and light. Measuring a heat signal and its corresponding scintillating light, allows event-by-event particle identification down to certain energies. Therefore, the development of cryogenic light detectors that can achieve single photon sensitivity, have high radio-purity and excellent energy resolution, is a key point to improve the experiment's sensitivity at low energies. In this contribution we explain and report on novel ways to improve the light collection efficiency through a preliminary study on Nb films sputtered on Sapphire and through highly doped Si as cryogenic light detectors.